الفهرس 
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Abstract
The present work was designed to study the therapeutic effect of intra-articular injection of PRP on the structure of the knee joint in a rat model of OA.
Forty adult male albino rats, weighing 200-250 gms, were used in this study, ten rats were used as donor to obtain PRP. The other thirty rats were divided into two main groups:
group (I) control group: consisted of 15 rats, subdivided into 3 subgroups:
Subgroup IA: (5 rats) were left without intervention and were sacrificed after 4 weeks from the beginning of the experiment.
Subgroup IB: (5 rats) were left without intervention and were sacrificed after 6 weeks from the beginning of the experiment.
Subgroup IC: (5 rats) were left for 4 weeks then received intra-articular injection of PRP (0.2 ml) in the right knee joint. The injections were repeated three times per week for 2 weeks then the animal were sacrificed.
group (II) osteoarthritis group: consisted of 15 rats, subjected to surgical procedure to induce osteoarthritis, then the rats were subdivided into 3 subgroups:
Subgroup (IIA): (5 rats) were sacrificed after 4 weeks of surgery.
Subgroup (IIB): (5 rats) were sacrificed after 6 weeks of surgery.
Subgroup (IIC): (5 rats) were received intra-articular injection of PRP (0.2 ml) in the right knee joints 4 weeks after surgery. The injections were repeated three times per week for 2 weeks then the animal were sacrificed.
At the end of the experiment, all animals were sacrificed and the right knee joints were dissected, trimmed of skin and muscles (soft tissues) and processed for the following histological techniques
1. Hematoxylin and Eosin stain (H&E).
2. Mallory stain.
3. Toluidine blue stain.
4. Immune-histochemical stain: for detection of platelet derived growth factor (PDGF) and vascular endothelial growth factor (VEGF).
5. Transmission electron microscope of the synovial membrane and articular cartilage of the knee joint.
Also, the morphometric and statistical measurements were done.
Histological examination of H&E stained sections of OA groups (subgroups IIA and IIB) showed thickening of the intimal lining with synovial fold formation and cellular infiltration of subintima. Surface erosions of the articular cartilage, discontinuity of matrix, areas of chondrocytes loss and an apparent decrease in the thickness of the articular cartilage were observed.
On the other hand, in subgroup IIC, the articular surface was relatively smooth, and the chondrocytes were almost organized into layers. The synovial membrane showed an apparent decrease in the intimal lining compared to subgroups IIA and IIB with evident fat cells in the subintimal stroma.
There was a significant decrease in the mean cartilage thickness of subgroups IIA and IIB when compared with the control subgroups IA and IC and there was a significant decrease in the mean cartilage thickness in subgroup IIB as compared with subgroup IIA.
The synovial membrane stained with mallory stain revealed abundant collagen fibers in the subintimal stroma in subgroups IIA and IIB, while in subgroups IIC, relatively few collagen fibers were detected.
There was a significant increase in the mean area percentage of collagen in animals of subgroups IIA and IIB when compared with the control subgroups IA and IC. Likewise a significant increase was detected in subgroup IIB as compared to subgroup IIA. Conversely, the mean area percentage of collagen revealed a significant decrease in subgroup IIC as compared to subgroups IIA and IIB.
Toluidine blue stained sections demonstrated faint staining of the cartilage matrix in subgroups IIA and IIB, whereas, subgroups IIC showed increased staining of the matrix.
There was a significant decrease in the mean color density of toluidine blue stain in animals of subgroups IIA and IIB as compared to the control subgroups IA and IC. On the other hand, color density of toluidine blue was significantly increased in subgroup IIC in comparison to subgroups IIA and IIB.
Immunohistochemically stained sections with PDGF and VEGF showed strong expression in the cytoplasm of synoviocytes and in the cytoplasm of vascular endothelium in subgroups IC and IIC. However, in subgroups IIA and IIB, the expression was moderate while in subgroups IA and IB was weak.
There was a significant decrease in PDGF and VEGF expression in animals of subgroup IA when compared with subgroups IC and IIC. Similarly, there was a significant decrease in PDGF and VEGF expression in subgroups IIA and IIB as compared to subgroups IC and IIC. Moreover, there was a significant increase in subgroups IC and IIC in comparison to subgroups IIA, IIB and IA.
Transmission electron microscopic study of the right knee joints of subgroups IIA and IIB showed shrunken chondrocyte with deformed nucleus. The cell membrane was irregular and the cytoplasm showed multiple vacuoles. Meanwhile subgroup IIC showed a chondrocyte with euchromatic nucleus and filling the lacuna.
All the histological changes in OA group were more evident in subgroup IIB than in subgroup IIA.
Conclusion
Intra-articular injection of PRP could effectively restore the structure of articular cartilage and synovial membrane of the knee joint of the rats of subgroup IIC.
RECOMMENDATIONS
• Intra-articular PRP injection might represent a promising new therapeutic strategy that assists the repair of the articular cartilage. So, further studies are recommended to investigate the effect of repeated intra-articular PRP injection and for longer duration.
• Moreover, concomitant administration of PRP with intra-articular corticosteroids, or hyalouronic acid, or stem cells might lead to hopeful results in severe knee joint osteoarthritis.